This book constitutes the thoroughly refereed post-proceedings of the 12th International Monterey Workshop on Networked Systems with special focus on realization of reliable systems on top of unreliable networked platforms, held in Laguna Beach, CA, USA, in September 2005. The 6 revised full papers presented together with 10 papers contributed by the invited speakers were carefully selected during two rounds of reviewing and improvement from numerous submissions. Major issues covered by the workshop contributions are model-based software development of network-centric system-of-systems, foundations of future design and programming abstractions, active fault management in network-centric systems, intelligent and robust middleware, as well as model-based development of certifiable systems.